1. Field of the Invention
Apparatuses consistent with the present invention relate to wireless communication elements for mobile communication devices, and more particularly, to ultrahigh-frequency resonators, band-pass filters, and duplexers for mobile communication devices.
2. Description of the Related Art
With the trend of miniaturization and high functionality of mobile communication terminals, the technology for manufacturing high-frequency components for mobile communication terminals has been rapidly developed. A filter is a core component of a high-frequency mobile communication device. This filter is used to select a desired signal or to filter a specific signal among many sky-wave signals. As the frequency band of the mobile communication terminal increases, the need for an ultrahigh-frequency device increases. However, when an ultrahigh-frequency device is used in a mobile communication terminal, it is difficult to miniaturize and manufacture the mobile communication terminal with low costs. For example, an ultrahigh-frequency resonator (or filter) operating at a frequency of 2 GHz or more is too large to be integrated using a dielectric resonator such as a related art coaxial ceramic resonator. A surface acoustic wave (SAW) resonator is used instead of the dielectric resonator. However, the SAW resonator has high insertion loss and is difficult to integrate and miniaturize. In order to address these problems, much research has been conducted on the use of a film bulk acoustic wave resonator (FBAR) or a thin film resonator (TFR), which operates according to the thickness vibration of a piezoelectric thin film.
However, there still is need for a mobile communication device that can operate at an ultrahigh frequency of 4 GHz or more, be miniaturized and manufactured with low costs, since the related art FBAR does not satisfy such requirements.